Caspian Gull adult

In recent weeks there has been some great gull watching at Burrowes Pit on the RSPB Reserve and many great photos on Martins Blog PLODDINGBIRDER have incentivised a few visiting birders to start looking for Caspian and Yellow-legged Gulls. The recent totals of these two species (to date at Least 20 Caspian Gulls and nine Yellow-legged Gulls) mainly using Burrowes Pit, has given plenty of opportunities to try and identify various ages of Caspian and Yellow-legged Gull against the commoner species of Great and Lesser Black-backed and Herring Gulls.

I'm still a relative newcomer in respect of having the opportunity to sit and look through gulls and whilst many birders ignore gulls as too difficult, they are a fun and rewarding group on which to hone your identification skills. In this blog post and maybe a couple of other posts, i've tried  to provide a little bit of  information on identification features for Caspian and Yellow-legged Gull, mainly for my own benefit to understand if i'm getting it right or wrong along with a chance to compare and use the identification literature against my photos. So, if you want to, please feel free to comment on my id attempts and associated reasoning.

December 8th

In the shot below, there is an adult Caspian Gull which is just taking off and three Yellow-legged Gulls, a 3CY flying, a 2CY to the left of the adult Caspian Gull and an adult (third gull in from the right that is partially obscured). 

1.The adult Caspian Gull (before it took off), whilst showing the beady dark eye and lovely smallish pure white rounded head and long/pointed parallel billed head profile, has pale yellowish legs.

2.The yellowish looking legs confused me until I read much later that adults have pale yellow legs (in summer). Luckily other features to aid identification of adult Caspian Gull became more obvious when it flew. 

3.Primary 10 (P10) shows a long white tongue with very little black near the tip. Whilst this feather looks old, it is a typical adult feature. On the upperwing you can only just make out a narrow portion of the tongue but on the underwing, whilst still only a narrow section is visible you can see that it is long and whitish. There are also long white mirrors on P10 and P9, something which adult Yellow-legged Gulls don't show on P9. 

4.Another feature to support adult Caspian Gull is the presence of a tick mark on P4. In this photo the features on P10 and P9 are obscured. I reckon there is another possible feature in that the underwing is very pale with little contrast between the primaries, secondaries and underwing coverts. So, despite thinking this adult gull has dull yellow legs and pinkish feet, other features are good for supporting adult Caspian Gull. 

5.Adult Caspian Gull (left) and a 2CY Yellow-legged Gull (right)